Methods and apparatus for discovering a powerability condition of a computer network

ABSTRACT

The invention is directed to techniques for discovering a powerability condition of a computer network such as the existence of a remotely powerable device attached to a connecting medium of the computer network. Such detection can then control whether a remote power source (e.g., a data communications device such as a switch) provides remote power (e.g., phantom power) to the computer network. One arrangement of the invention is directed to an apparatus for discovering a powerability condition of a computer network. The apparatus includes a signal generator, a detector and a controller which is coupled to the signal generator and the detector. The controller configures the signal generator to provide a test signal to a connecting medium of the computer network, and configures the detector to measure a response signal from the connecting medium of the computer network. The controller then indicates whether a remotely powerable device connects to the connecting medium of the computer network based on the response signal. Accordingly, if the apparatus discovers a remotely powerable device attached to the computer network (i.e., the power requirement condition of the network), the apparatus can provide power to the device remotely (e.g., through the connecting medium). However, if the apparatus does not discover a remotely powerable device attached to the computer network (e.g., another power requirement condition), the apparatus can avoid providing power remotely and thus avoid possibly damaging any non-remotely powerable device on the computer network.

BACKGROUND OF THE INVENTION

There is a wide variety of data communications networks suitable forcarrying data between devices. For example, Ethernet is a widely usedarchitecture for local-area networks (LANs). The architecture for such acomputer network, along with variants defined in the IEEE 802.3standard, is the result of work performed at a variety of companies.

Initially, the purpose of an 802.3 network was to carry datacommunications exclusively. All of the devices attached to such acomputer network included their own power supplies and derived powerfrom these power supplies. Accordingly, each device operated as astandalone system with unlimited local power.

Today, there exists a wide range of devices for which remotepowerability is highly desirable. For example, it would be convenient ifcertain devices, which can attach to an 802.3 network, could draw powerfrom the 802.3 network in order to operate properly. Examples of suchdevices include Internet telephones (IP phones) andsecurity/surveillance devices.

SUMMARY OF THE INVENTION

Unfortunately, if a power source (e.g., a power supply) simply appliespower to an 802.3 computer network in order to power a remotelypowerable device on that network, there is a high risk of damaging anynon-remotely powerable device on the network, i.e., a device which doesnot require and draw remote power. A conventional non-remotely powerabledevice typically includes circuitry (e.g., a network terminationcircuit) that is unable to handle power provided over a computernetwork. In the event of remote power application, such circuitry canoverheat or burn out resulting in permanent damage to the non-remotelypowerable device.

Furthermore, applying power to a computer network that does not requiresuch power runs the risk of creating adverse conditions within thecomputer network itself. For example, applying power to an 802.3 networkruns the risk of generating broadcast firestorms within the 802.3network.

In contrast, the invention is directed to techniques for discovering apowerability condition of a computer network such as the existence of aremotely powerable device attached to a connecting medium of thecomputer network. Such detection can then control whether a remote powersource (e.g., a data communications device such as a switch, or amid-span device such as a patch panel) provides remote power to thecomputer network (e.g., phantom power from a VDC power source connectedto digital communication lines of the network, direct power, etc.).

One arrangement of the invention is directed to an apparatus fordiscovering a powerability condition of a computer network. Theapparatus includes a signal generator, a detector, and a controllerwhich is coupled to the signal generator and the detector. Thecontroller configures the signal generator to provide a test signal to aconnecting medium of the computer network, and configures the detectorto measure a response signal from the connecting medium of the computernetwork. The controller then indicates whether a remotely powerabledevice connects to the connecting medium of the computer network basedon the response signal. Accordingly, if the apparatus discovers aremotely powerable device attached to the computer network (i.e., apowerability condition of the network), the apparatus can provide powerto the device remotely (e.g., through the connecting medium). However,if the apparatus does not discover a remotely powerable device attachedto the computer network (e.g., another powerability condition of thenetwork), the apparatus can avoid providing power remotely and thusavoid possibly damaging any non-remotely powerable devices on thecomputer network.

In one arrangement, the computer network supports connection of aremotely powerable device that receives, during normal operation, anoperating voltage having a first voltage magnitude. Here, the controllerconfigures the signal generator to supply, as the test signal, a testvoltage having a second voltage magnitude that is substantially lessthan the first voltage magnitude. Accordingly, if there is no remotelypowerable device connecting to the computer network but there is anon-remotely powerable device that connects to the computer network, thecurrent resulting from the application of the second (lower magnitude)test voltage is less likely to cause damage to the non-remotelypowerable device compared to the current that would result from theapplication of the first (higher magnitude) test voltage.

In one arrangement, the controller configures the signal generator tosupply, to the connecting medium, (i) a first voltage during a firsttime period, and (ii) a second voltage that is substantially differentthan the first voltage during a second time period. Preferably, thecontroller configures the signal generator to apply one of a positiveand negative test voltage to the connecting medium as the first voltage(e.g., −5 volts), and the other of the positive and negative testvoltage to the connecting medium as the second voltage (e.g., +5 volts).This arrangement enables the controller to determine whether a remotedevice, which allows current to flow when in only one direction (e.g., aremotely powerable device), connects to the computer network and, if so,whether that device is properly connected (or reverse-wired).

In one arrangement, the connecting medium includes (i) a firstconnecting link having a local end that terminates at a firsttransformer and a remote end, and (ii) a second connecting link having alocal end that terminates at a second transformer and a remote end. Inthis arrangement, the controller preferably configures the signalgenerator to apply the test signal to the connecting medium through acentertap of the first transformer and a centertap of the secondtransformer. This arrangement is particularly advantageous in 802.3networks since such networks typically use centertapped transformersthus enabling the invention to utilize existing network-relatedcomponents.

In one arrangement, the connecting medium includes a local end and aremote end. Preferably, the controller selectively identifies, throughthe local end of the connecting medium, one of (i) a backwards wireddevice condition at the remote end, (ii) an open condition at the remoteend, (iii) a remotely powerable device condition at the remote end, and(iv) a shorted/non-powerable device condition at the remote end.Accordingly, the controller can distinguish between a variety ofcomputer network conditions (i.e., powerability conditions).

One arrangement of the invention is directed to a data communicationsdevice (e.g., a switch, a hub, a router, a bridge, etc.) or other device(e.g., a patch panel) that includes normal operating circuitry whichcommunicates with a remote device over a computer network during normaloperation, and power circuitry coupled to the normal operatingcircuitry. In this arrangement, the power circuitry, which is capable ofdiscovering whether the remote device is remotely powerable over thecomputer network, is built into the data communications device itself.

Another arrangement of the invention is directed to a remotely powerabledevice having normal operating circuitry which couples to a connectingmedium of a computer network, and a powerability indicator which couplesto the normal operating circuitry. The powerability indicator is capableof receiving a test signal from the connecting medium of the computernetwork, and providing a response signal to the connecting medium of thecomputer network to enable discovery of the remotely powerable devicebased on the response signal.

Another arrangement of the invention is directed to a computer programproduct that includes a computer readable medium having instructionsstored thereon for discovering a powerability condition of a computernetwork. The instructions, when carried out by a processor, cause theprocessor to perform the steps of: (i) providing a test signal to aconnecting medium of the computer network; (ii) measuring a responsesignal from the connecting medium of the computer network; and (iii)determining whether a remotely powerable device connects to theconnecting medium of the computer network based on the response signal.

The features of the invention, as described above, may be employed indata communications devices and other computerized devices such as thosemanufactured by Cisco Systems, Inc. of San Jose, Calif.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a block diagram showing a remote powerability system which issuitable for use by the invention.

FIG. 2 is a flow diagram illustrating a procedure performed by a powerapparatus of FIG. 1.

FIG. 3 is a block diagram showing an arrangement of components which issuitable for use for forming a portion of the remote powerability systemof FIG. 1.

FIG. 4 is a flow diagram illustrating a procedure which is suitable foruse as a step of providing a test signal and measuring a response signalof FIG. 2.

FIG. 5 is a circuit diagram showing certain circuit element detailswhich are suitable for use in particular components of FIG. 3.

FIG. 6A is a block diagram showing a component arrangement having anopen condition for comparison to the arrangement of FIG. 3.

FIG. 6B is a block diagram showing a component arrangement having abackwards wired device condition for comparison to the arrangement ofFIG. 3.

FIG. 6C is a block diagram showing a comparison to the arrangement ofFIG. 3.

FIG. 7 is a block diagram showing a component arrangement having aremote powerability system of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A remotely powerable device is a device which requires and draws powerfrom a remote power source for normal operation. The invention isdirected to techniques for discovering a powerability condition of acomputer network such as the existence of a remotely powerable deviceattached to a connecting medium of the network. Such detection can thencontrol whether a remote power source (e.g., a data communicationsdevice such as a switch) provides remote power (e.g., phantom power ordirect power) to the network. That is, if it is determined that aremotely powerable device is attached to the network, the remote powersource can provide power to the device remotely (e.g., through theconnecting medium). However, if no remotely powerable device isdiscovered, the remote power source can avoid providing power remotely,and thus avoid possibly damaging any non-remotely powerable devices onthe network. Such techniques may be employed in data communicationsdevices and other computerized devices such as those manufactured byCisco Systems, Inc. of San Jose, Calif.

FIG. 1 shows a remote powerability system 20 which is suitable for useby the invention. The system 20 is a computer network which includes adevice 22-A (e.g., an IP phone) and a device 22-B (e.g., an IP switch).The devices 22-A, 22-B (collectively, devices 22) communicate with eachother through a connecting medium 24. In one arrangement, the devices 22include physical layer devices (PHY), and the connecting medium 24includes a Medium Dependent Interface (MDI) having multiple lines forcarrying signals between the devices 22 (e.g., 10BaseT, 100BaseT, etc.).The system 20 further includes a power apparatus 26 which connects withthe device 22-B through connections 28. The power apparatus 26 includesa controller 30, a signal generator 32 and a detector 34. Furtherdetails of the invention will now be discussed with reference to FIG. 2.

FIG. 2 shows a procedure 40 which is performed by the power apparatus 26in order to discover a powerability condition of the system 20 of FIG.1. In particular, the power apparatus 26 performs the procedure 40 todetermine whether the device 22-A is remotely powerable.

In step 42, the apparatus 26 provides a test signal (e.g., multiplevoltages) to the connecting medium 24, and measures a response signal(e.g., current in response to the multiple voltages). In particular, thecontroller 30 configures the signal generator 32 to provide the testsignal to the connecting medium 24 of the system 20 through the device22-B. Additionally, the controller 30 configures the detector 34 tomeasure the response signal from the connecting medium 24 through thedevice 22-B.

In step 44, the apparatus 26 indicates whether a remotely powerabledevice connects to the connecting medium 24 based on the responsesignal. In particular, the controller 30 stores an indication signalresult of the detector 34 which is based on the response signal. Theindication signal result indicates whether the device 22-A is a remotelypowerable device.

In step 46, the apparatus 26 proceeds to step 48 if it discovers that aremotely powerable device connects to the connecting medium 24.Otherwise (i.e., if the apparatus 26 does not discover a remotelypowerable device connecting to the connecting medium 24), the apparatus26 proceeds to step 50.

In step 48, when the apparatus 26 has discovered that the device 22-A isremotely powerable, the apparatus 26 provides power to the device 22-A.As will be explained in further detail later, the apparatus 26preferably provides phantom power to the device 22-A through theconnecting medium 24. The apparatus 26 then terminates the procedure 40.

In step 50, when the apparatus 26 has not discovered a remotelypowerable device connecting to the system 20, the apparatus 26determines whether it should continue operation. If not, the apparatus26 terminates the procedure 40 (e.g., in response to a shutdown or resetcommand). If the apparatus 26 determines that it should continueoperation, the apparatus 26 proceeds to step 52.

In step 52, the apparatus 26 allows a delay time period to elapse, andthen proceeds back to step 42 to repeat the procedure 40. In onearrangement, the apparatus 26 waits a relatively short period of time(e.g., one to two minutes) before proceeding In back to step 42.

FIG. 3 is a block diagram showing, by way of example only, anarrangement 60 of components which is suitable for use for the remotepowerability system 20 of FIG. 1. Each device 22 includes normaloperating circuitry 62 and a set of transformers 64, 66. Eachtransformer 64, 66 includes a centertap 68 that divides a portion of thetransformer 64,66 into an upper coil and a lower coil, and providesdirect access to the connecting medium 24.

The invention relies on distinguishing connection attributes between (i)a remotely powerable device at a remote end of a network connection,(ii) a reverse-wired remotely powerable device at a remote end of anetwork connection, (iii) an open condition at a remote end of a networkconnection, and (iv) a non-remotely powerable device at a remote end ofa network connection or a short in the network connection. In onearrangement, the remotely powerable device allows current to flow inonly one direction through the network connection, the reverse-wiredremotely powerable device allows current to flow only in the oppositedirection, the open condition prevents current from flowing in eitherdirection, and the non-remotely powerable device/shorted-conditionallows current to flow in both directions.

As shown in FIG. 3, the device 22-A is a remotely powerable device whichincludes a powerability indicator formed by a diode 70 and a resistor 72connected in series between the centertaps 68 of the transformers 64-Aand 66-A. The powerability indicator provides, in response to a testsignal, a response signal to the connecting medium 24 indicating thatthe device 22-A is remotely powerable. In particular, the powerabilityindicator allows current to flow in only one direction (i.e., from thetransformer 64-A to the transformer 66-A) which uniquely characterizesthe device 22-A as a remotely powerable device. In contrast,non-remotely powerable devices typically allow current flow in bothdirections.

As further shown in FIG. 3, the power apparatus 26 connects to thecentertaps 68 of the transformers 64-B and 66-B of the device 22-Bthrough the connections 28. The power apparatus 26 provides the testsignal to the connecting medium 24 and receives the response signal fromthe connecting medium 24 through these connections 28 and the centertaps68 of these transformers 64-B and 66-B.

The connecting medium 24 includes multiple lines 76, 78. In onearrangement, the connecting medium 24 uses 802.3 based technology (e.g.,10BaseT, 100BaseT, etc.). In this arrangement, the connecting medium 24(e.g., Category 5 cabling) includes twisted pair wiring 76-1, 76-2(e.g., for carrying a differential signal pair between the device 22-Aand the device 22-B) and twisted pair wiring 78-1, 78-2 (e.g., forcarrying a differential signal pair between the device 22-B and thedevice 22-A). The connecting medium 24 connects to the devices 22through connectors 74 (e.g., RJ45 plugs and adaptors). When the remotelypowerable device 22-A is properly connected to the connecting medium 24,the powerability indicator of the remotely powerable device 22-A (thediode 70) allows current to flow only in one direction, from lines 76-1,76-2 to lines 78-1, 78-2.

The power apparatus 26, as shown in FIG. 3, includes control circuitry80 and several direct current (DC) power supplies and switches. Inparticular, the power apparatus 26 includes a −48 volt (V) DC powersupply 82 which is controllable by a switch 84, a −5 VDC power supply 86which is controllable by a switch 88, and a +5 VDC power supply 90 whichis controllable by a switch 92. The control circuitry 80 and switches84, 88 and 92 form the controller 30 (see FIG. 1). The power supplies82, 86 and 90 form the signal generator 32 (again, see FIG. 1). Thepower apparatus 26 further includes current detectors 94-1 and 94-2which form the detector 34 (FIG. 1).

The control circuitry 80 is capable of selectively supplying −48 volts,−5 volts and +5 volts to the connecting medium 24 by operating theswitches 84, 88 and 92. In particular, when the control circuitry 80opens switches 84, 92 and closes the switch 88, the power supply 86provides −5 volts to the connecting medium 24 in order to measure acurrent response (the response signal). Similarly, when the controlcircuitry 80 opens switches 84, 88 and closes the switch 92, the powersupply 90 provides +5 volts to the connecting medium 24 in order tomeasure another current response. Additionally, when the controlcircuitry 80 opens switches 88, 92 and closes the switch 84, the powersupply 82 provides −48 volts to the connecting medium 24 in order toprovide phantom power to the device 22-A which connects to the remoteend of the connecting medium 24. It should be understood that thedevices 22-A and 22-B can communicate with each other through theconnecting medium 24 using differential pair signals while the powersupply 82 applies power to the device 22-A through the connecting medium24, i.e., while the device 22-A draws phantom power from the powerapparatus 26 through the connecting medium 24.

Furthermore, it should be understood that the power supplies 86, 90 arepreferably low current power supplies, i.e., capable of limiting thecurrent to less than an amp (e.g., 25-30 milliamps) in order to preventdamaging any non-remotely powerable devices connecting to the connectingmedium 24.

In one arrangement, the control circuitry 80 includes a data processingdevice or processor. Here, a computer program product 98 (e.g., one ormore CDROMs, tapes, diskettes, etc.) provides instructions which directthe operation of the processor. Alternatively, the processor acquiresthe instructions through other means, e.g., via a network downloadthrough the device 22-B, or has non-volatile storage associated with theprocessor (e.g., ROM, flash memory, etc.). Further details of theoperation of the remote power system 20 will now be provided withreference to FIGS. 4 and 5.

FIG. 4 shows a procedure 100 which is suitable for use as step 42 of theprocedure 40 (FIG. 2) performed by the power apparatus 26. The procedure100 involves providing a test signal (e.g., multiple voltages) to theconnecting medium 24 and measuring a response signal (e.g., current).

In step 102, the power apparatus 26 begins supplying, to the connectingmedium 24, a first voltage during a first time period. In particular,the control circuitry 80 closes the switch 88 for 100 milliseconds suchthat the −5 VDC power supply 86 applies −5 volts across the centertaps68 of the transformers 64-B and 66-B. As a result, −5 volts appearsacross the diode 70 of the device 22-A which reverse biases the diode70.

In step 104 and during the first time period, the power apparatus 26measures current through the connecting medium 24. In particular, thecontrol circuitry 80 activates the current detector 94-2 to determinewhether current flows through the connecting medium 24. Since the diode70 is reversed biased, no current flows through the connecting medium24, and the control circuitry 80 detects no current flow. FIG. 5 shows acircuit diagram having circuit elements which are suitable for use forthe current detector 94-2.

In one arrangement, the procedure 100 does not include step 106 and step104 proceeds to step 108. However, in another arrangement, the procedure100 includes step 106 which allows the power apparatus 26 to terminatethe procedure 100 if it determines that there is no remotely powerabledevice properly connecting to the connecting medium 24. In particular,in step 106, the power apparatus 26 determines whether the responsesignal indicates that a properly connected remotely powerable devicepossibly exists on the connecting medium 24. If so, step 106 proceeds tostep 108. If not, the procedure 100 terminates.

In step 108, the power apparatus 26 begins supplying, to the connectingmedium 24, a second voltage during a second time period. In particular,the control circuitry 80 of the power apparatus 26 closes the switch 92for 100 milliseconds such that the +5 VDC power supply 90 applies +5volts across the centertaps 68 of the transformers 64-B and 66-B. As aresult, +5 volts appears across the diode 70 of the device 22-A whichforward biases the diode 70.

In step 110 and during the second time period, the power apparatus 26measures current through the connecting medium 24. In particular, thecontrol circuitry 80 activates the current detector 94-1 to determinewhether current flows through the connecting medium 24. Since the diode70 is forward biased, current flows through the connecting medium 24,and the control circuitry 80 detects this current flow. The circuitdiagram of FIG. 5 includes circuit elements which are suitable for usefor the current detector 94-1.

After step 110, the procedure 100 terminates. The results of theprocedure 100 can be used by the control circuitry 80 to determinewhether to provide power to the connecting medium 24. For example, thecharacteristic of allowing current to flow in only one direction fromlines 76 to lines 78 (FIG. 3) indicates that the device 22-A is aremotely powerable device. Accordingly, during steps 46 and 48 of FIG.2, the power apparatus 26 provides phantom power to the remotelypowerable device 22-A through the connecting medium 24.

As stated above, FIG. 5 shows a circuit diagram which includes circuitrywhich is suitable for use for each of the current detectors 94-1 and94-2. The current detector 94 includes a resistor 124 and a comparator126 having its inputs connected to the ends of the resistor 124.Accordingly, as current flows through the connecting medium 24 andthrough the resistor 124, the potential difference across the resistor124 is applied to the inputs of the comparator 126. The comparator 126provides an indication signal 128 indicating whether the potentialdifference exceeds a predetermined voltage threshold, i.e., whetherthere is current flow through the connecting medium 24.

It should be understood that one skilled in the art can select asuitable value for the resistor 124 (e.g., 10 ohms) in order to properlygenerate the indication signal 128. For example, suppose that eachtransformer 64, 66 provides approximately 20 ohms of resistance so thateach half coil provides 10 ohms of resistance. Further suppose that theconnecting medium is 26 gauge medium hardness wire having a resistanceof 42.4 ohms per foot and that the maximum length of the connectingmedium 24 is 100 meters (approx. 328 feet) thus translating into amaximum resistance per wire of 13.9 ohms. The resulting resistance fromthe power apparatus 26, through the transformer 64-B (5 ohms), throughthe wires 76 (6.95 ohms), through the transformer 64-A (5 ohms), throughthe diode 70 (31 ohms if the current is limited to about 25 milliamps),through the resistor 72 (100 ohms), through the transformer 66-A (5ohms), through the wires 78 (6.95 ohms), through the transformer 66-B (5ohms), and through the resistor 124 (10 ohms) is 174.9 ohms. If theapplied voltage is −5 volts, the current flow is approximately 28.6milliamps (−5 volts divided by 174.9 ohms). Accordingly, the voltagedrop across the sensing resistor 124 approximately 286 millivolts (10ohms times 28.6 milliamps) which is a value that is easily detectable bythe comparator 126 in order to properly provide the indication signal128.

Additionally, it should be understood that the power apparatus 26 iscapable of discovering other powerability conditions of the system 20 ofFIG. 1, i.e., of the computer network. In particular, the powerapparatus 26 can determine (i) when there is no device connecting to theconnecting medium 24 at the remote end, (ii) when there is areverse-wired remotely powerable device connecting to the connectingmedium 24 at the remote end, and (iii) when there is a shorted conditionor non-remotely powerable device connected to the connecting medium 24at the remote end. As stated above, when there is no device at theremote end of the connecting medium 24, there is no possible currentflow through the connecting medium 24 in either direction. When there isa reverse-wired remotely powerable device at the remote end of theconnecting medium 24, there is current flow when only in one directionwhich is opposite to the direction of current flow for a properlyconnected remotely powerable device. When there is a short in theconnecting medium 24 or a non-remotely powerable device at the remoteend, current is capable of flowing in both directions. Further detailsof how the power apparatus 26 makes such determinations will now beprovided with reference to FIGS. 6A, 6B and 6C.

FIG. 6A shows an arrangement 130 in which there is no device at theremote end of the connecting medium 24, and in which an open condition132 exists at the remote end of the connecting medium 24. Accordingly,current cannot flow in either direction through the connecting medium24.

For the arrangement 130, the power apparatus 26 performs the procedure40 (FIG. 2). In step 42 of the procedure 42, the power apparatus 26provides a test signal to the connecting medium 24, and measures aresponse signal. In particular, the power apparatus 26 performs theprocedure 100 for step 42 (FIG. 4). That is, the power apparatus 26supplies −5 volts to the connecting medium 24 (step 102). Since nocurrent flows through the connecting medium 24 due to the open condition132 at the remote end, the power apparatus 26 measures no current flow(step 104).

Recall that if the remotely powerable device 22-A were properlyconnected to the remote end of the connecting medium 24 (FIG. 3), thepower apparatus 26 would also detect no current flow due to the reversebiasing of the diode 70 of the device 22-A. Since the power apparatus 26cannot yet distinguish between the open condition 132 and a presence ofa remotely powerable device 22-A, the power apparatus 26 does not yetconclude that the open condition 132 exists at the remote end.

The power apparatus then supplies +5 volts to the connecting medium 24(step 108 of FIG. 4). Again, the power apparatus 26 measures no currentflow (step 110), since no current flows through the connecting medium 24due to the open condition 132 at the remote end. If a remotely powerabledevice 22-A had been connected to the connecting medium 24 at the remoteend, current would have flowed through the connecting medium 24 and thedevice 22-A. Since the power apparatus 26 detects no current flow ineither direction, the power apparatus 26 concludes that there is theopen condition 132 at the remote end of the connecting medium 24 anddoes not supply an operating voltage (e.g., −48 volts) to the connectingmedium 24.

FIG. 6B shows an arrangement 140 in which there is a backwards-wired, orreverse-wired, remotely powerable device 22-A at the remote end of theconnecting medium 24. Accordingly, current can flow only in onedirection which is opposite to the direction of current flow for aproperly connected remotely powerable device.

For the arrangement 140, the power apparatus 26 performs the procedure100 to provide a test signal to the connecting medium 24 and measure aresponse signal (also see step 42 of FIG. 2). That is, the powerapparatus 26 supplies −5 volts to the connecting medium 24 (step 102 ofFIG. 4) which forward biases the diode 70 of the reverse-wired remotelypowerable device 22-A. Accordingly, current flows through the connectingmedium 24, and the power apparatus 26 measures this current flow (step104). The presence of (i) a short in the connecting medium 24, (ii) areverse-wired remotely-powerable device 22-A at the remote end, or (iii)a non-remotely powerable device at the remote end could cause current toflow through the connecting medium 24 during this phase.

In contrast, if the remotely powerable device 22-A were properlyconnected to the remote end of the connecting medium 24 (FIG. 3), thepower apparatus 26 would detect no current flow due to the reversebiasing of the diode 70 of the device 22-A. Accordingly, the powerapparatus 26 concludes that there is not a properly connected remotelypowerable device at the remote end of the connecting medium 24. In onearrangement, the power apparatus 26 terminates the procedure 100 at thispoint (step 106). In another arrangement, the power apparatus 26continues the procedure 100.

If the power apparatus 26 continues the procedure 100, the powerapparatus 26 supplies +5 volts to the connecting medium 24 (step 108)which reverse biases the diode 70 of the reverse-wired remotelypowerable device 22-A. Accordingly, the power apparatus 26 measures nocurrent flow through the connecting medium 24 (step 110). A short in theconnecting medium 24 or the presence of a non-remotely powerable devicewould have resulted in current flow in the connecting medium 24 duringthis phase. Since the power apparatus 26 detects current flow only inone direction which is opposite to the direction of current flow for aproperly connected remotely powerable device, the power apparatus 26concludes that a reverse-wired remotely powerable device 22-A exists atthe remote end of the connecting medium 24.

FIG. 6C shows an arrangement 150 in which there is a non-remotelypowerable device 152 at the remote end of the connecting medium 24 (oralternatively a short in the connecting medium 24). The non-remotelypowerable device 152 is a conventional device having its own powersupply and can be characterized as including transformers 154-A, 156-A,series-connected resistances 158, 160 (e.g., 75 ohms each) betweencentertaps of the transformers 154-A, 156-A, and a capacitance 162interconnected between ground 164 and an intermediate node of theseries-connected resistances 158, 160. The series-connected resistancesallow current to flow in both directions through the connecting medium24.

For the arrangement 150, the power apparatus 26 performs the procedure100 to provide a test signal to the connecting medium 24 and measure aresponse signal (also see step 42 of FIG. 2). In particular, the powerapparatus 26 attempts to supply −5 volts to the connecting medium 24(step 102 of FIG. 4). In response, current flows through the connectingmedium 24 and through the series-connected resistances 158, 160, and thepower apparatus 26 measures this current flow (step 104).

If the remotely powerable device 22-A were properly connected to theremote end of the connecting medium 24 (FIG. 3), the power apparatus 26would detect no current flow due to the reverse biasing of the diode 70of the device 22-A. Accordingly, the power apparatus 26 concludes thatthere cannot be a properly connected remotely powerable device at theremote end of the connecting medium 24. The cause of the current flowcould be (i) a short in the connecting medium 24, (ii) the presence of areverse-wired remotely powerable device at the remote end of theconnecting medium 24, or (iii) the presence of a non-remotely powerabledevice at the remote end of the connecting medium 24. In onearrangement, the power apparatus 26 terminates the procedure 100 at thispoint (step 106). In another arrangement, the power apparatus 26continues the procedure 100.

If the power apparatus 26 continues the procedure 100, the powerapparatus 26 supplies +5 volts to the connecting medium 24 (step 108)which, again, results in current flow through the connecting medium 24and the series connected resistances 158, 160. Accordingly, the powerapparatus 26 measures current flow through the connecting medium 24(step 110). The presence of a reverse-wired remotely powerable device atthe remote end of the connecting medium would-have resulted in nocurrent flow during this phase. Since the power apparatus 26 detectscurrent flow in both directions, the power apparatus 26 concludes thatthere exists either a non-remotely powerable device connected to theconnecting medium 24 at the remote end, as shown in FIG. 6C, or thatthere is a shorted condition in the connecting medium 24.

As described above, the power apparatus 26 is capable of discovering avariety of powerability conditions of the computer network, i.e., of thesystem 20. In one arrangement, the power apparatus 26 includes an outputdevice (e.g., an LED display) that indicates the detection of particularpowerability conditions (i.e., the conditions of FIGS. 6A, 6B and 6C) ofthe computer network. Further details of the invention will now beprovided with reference to FIG. 7 which shows an implementation of theinvention in a particular network topology (e.g., a hub-and-spokeconfiguration).

FIG. 7 shows a computer network 170 having a data communications device172 (e.g., an IP switch) and associated power apparatus 174 whichconnect with multiple devices 176-1, . . . , 176-N (collectively,devices 176) through connecting media 178-1, . . . , 178-N(collectively, connecting media 178). The power apparatus 174 performsthe procedure 40 for each connecting medium 178 to determine whether toprovide power to that connecting medium 178 (e.g., in a round robin orother multiplexed manner). If the power apparatus 174 discovers that aremotely powerable device connects to a remote end of a particularconnecting medium 178, the power apparatus 174 provides power remotelyto that device 178 (phantom power). Otherwise, the power apparatus 174does not provide remote power (to avoid damaging non-remotely powerabledevices) and waits a predetermined period of time (e.g., one to twominutes) and then rechecks that connecting medium 178 (see procedure 40in FIG. 2). For the devices 176 that are remotely powered by the powerapparatus 174 or have their own power sources (e.g., local powersources), the data communications device 172 communicates with thosedevices 176 over the respective connecting media 178. Accordingly, thecomputer network 170 enables data communications between devices andsafe application of remote power without risking damage to non-remotelypowerable devices.

As described above, the invention is directed to techniques fordiscovering a powerability condition of a computer network such as theexistence of a remotely powerable device attached to a connecting mediumof the computer network. Such detection can then determine whether aremote power source (e.g., a data communications device such as aswitch) provides remote power (e.g., phantom power) to the computernetwork. In particular, if it is determined that a remotely powerabledevice is attached to the computer network, the remote power source canprovide power to the device remotely (e.g., through the connectingmedium). However, if no remotely powerable device is discovered, theremote power source can avoid providing power remotely and thus avoidpossibly damaging any non-remotely powerable device on the computernetwork.

The invention leverages off of asymmetrical behavior of a remote device.If the application of stimuli to a computer network, which possibly hasa remote device connected thereto, results in expected behavior, powercan be safely applied to the remote device. However, if the behavior isnot as expected, power can be withheld and the unexpected behavior canbe identified. The features of the invention may be particularly usefulin computerized devices manufactured by Cisco Systems, Inc. of San Jose,Calif.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

For example, step 48 of the procedure 40 of FIG. 2 describes the powerapparatus 26 as providing power indefinitely to a remotely powerabledevice through the connecting medium 24. As an alternative, the powerapparatus 26 can intermittently confirm that the remotely powerabledevice is still connected to the remote end of the connecting medium 24.This alternative minimizes possible damage if the remotely powerabledevice is replaced with a non-remotely powerable device.

Additionally, it should be understood that the devices 22-A, 152 and 176can be a variety of communications devices such as IP phones,security/surveillance devices, etc. which are capable of drawing powerremotely. A powerability indicator (e.g., the diode 70 and the resistor72 series connected between centertaps 68 of the transformers 64-A,66-A) within each remotely powerable device provides an indication backto a remote power source (e.g., the power apparatus 26) that the deviceis remotely powerable.

Moreover, it should be understood that the devices 22-B, 172 can be avariety of communications devices as well such as Voice over IP (VoIP)switches, IP switches, hubs, routers, bridges, etc. The devices 22-B,172 can form a single device with the power apparatus 26, 174 or resideseparately from the power apparatus 26, 174. In one arrangement, thedevice 22-B, 172 is older equipment, and the power apparatus 26, 174connects the older equipment as an ancillary box.

Furthermore, it should be understood that FIG. 4 shows the powerapparatus 26 applying −5 volts to the connecting medium 24 (step 102)and then applying +5 volts to the connecting medium 24 (step 108), byway of example only. In another arrangement, the power apparatus 26applies +5 volts to the connecting medium 24 before applying −5 volts.In either arrangement, the power apparatus 26 indicates that a remotelypowerable device connects to the remote end of the connecting medium 24when the application of the +5 volts results in current flow, and theapplication of −5 volts results in no current flow (as measured in steps104 and 110). Of course, the system 20 can be reconfigured to indicatethat a remotely powerable device connects to the remote end of theconnecting medium 24 when the application of the −5 volts results incurrent flow, and the application of +5 volts results in no currentflow. Such modifications are intended to be within the scope of theinvention.

Additionally, it should be understood that the invention is suitable foruse in network topologies other than the hub-and spoke configuration ofFIG. 7. For example, the invention can be implemented in ringconfigurations that use point-to-point connections and terminationsbetween devices, and other configurations.

Furthermore, it should be understood that the power apparatus 26 can beconfigured to apply power to a remote device upon detection of areverse-wired remotely powerable device. For example, upon detection ofthe reverse-wired remotely powerable device 22-A of FIG. 6B, the powerapparatus 26 can be configured to provide power in a manner that enablesthe reverse-wired remotely powerable device 22-A to nevertheless operateproperly.

What is claimed is:
 1. A method for discovering a powerability conditionof a computer network, the method comprising the steps of: providing atest signal to differential signal lines of a connecting medium of thecomputer network; measuring a response signal from the differentialsignal lines of the connecting medium of the computer network; andindicating whether a remotely powerable device connects to theconnecting medium of the computer network based on the response signal;wherein the step of providing the test signal includes the steps of:supplying, to the connecting medium, a first voltage during a first timeperiod; and supplying, to the connecting medium, a second voltage thatis substantially different than the first voltage during a second timeperiod; wherein the step of supplying the first voltage includes thestep of: applying one of a positive and negative test voltage to theconnecting medium; and wherein the step of supplying the second voltageincludes the step of: applying the other of the positive and negativetest voltage to the connecting medium.
 2. The method of claim 1 whereinthe computer network supports connection of a remotely powerable devicethat receives, during normal operation, an operating voltage having afirst voltage magnitude; and wherein the step of providing the testsignal includes the step of: supplying, as the test signal, a testvoltage having a second voltage magnitude that is substantially lessthan the first voltage magnitude.
 3. The method of claim 1 wherein theconnecting medium includes a local end and a remote end, and wherein thestep of indicating includes the step of: selectively identifying,through the local end of the connecting medium, one of (i) a backwardswired device condition at the remote end, (ii) an open condition at theremote end, (iii) a remotely powerable device condition at the remoteend, and (iv) a shorted/non-powerable device condition at the remoteend.
 4. The method of claim 1 wherein the differential signal lines ofthe connecting medium include a first pair of differential signal linesconfigured to carry data signals between network devices and a secondpair of differential signal lines configured to carry other data signalsbetween the network devices, and wherein the step of providing the testsignal includes the step of: applying a DC voltage across the first andsecond pairs of differential signal lines.
 5. The method of claim 4wherein the step of applying the DC voltage includes the step of:coupling a signal generator between a centertap of the first pair ofdifferential signal lines and a centertap of the second pair ofdifferential signal lines.
 6. The method of claim 4, further comprisingthe step of: providing remote power to the computer network through thefirst and second pairs of differential signal lines to remotely power adevice.
 7. A method for discovering a powerability condition of acomputer network, the method comprising the steps of: providing a testsignal to a connecting medium of the computer network; measuring aresponse signal from the connecting medium of the computer network; andindicating whether a remotely powerable device connects to theconnecting medium of the computer network based on the response signal,wherein the connecting medium includes (i) a first connecting linkhaving a local end that terminates at a first transformer and a remoteend, and (ii) a second connecting link having a local end thatterminates at a second transformer and a remote end; and wherein thestep of providing the test signal includes the step of: applying thetest signal to the connecting medium through a centertap of the firsttransformer and a centertap of the second transformer.
 8. An apparatusfor discovering a powerability condition of a computer network,comprising: a controller; a signal generator coupled to the controller;and a detector coupled to the controller, the controller (i) configuringthe signal generator to provide a test signal to differential signallines of a connecting medium of the computer network, (ii) configuringthe detector to measure a response signal from the differential signallines of the connecting medium of the computer network, and (iii)indicating whether a remotely powerable device connects to theconnecting medium of the computer network based on the response signal;wherein the controller, when configuring the signal generator to providethe test signal, configures the signal generator to supply to theconnecting medium, (i) a first voltage during a first time period, and(ii) a second voltage that is substantially different than the firstvoltage during a second time period; and wherein the controllerconfigures the signal generator to apply one of a positive and negativetest voltage to the connecting medium as the first voltage, and theother of the positive and negative test voltage to the connecting mediumas the second voltage.
 9. The apparatus of claim 8 wherein the computernetwork supports connection of a remotely powerable device thatreceives, during normal operation, an operating voltage having a firstvoltage magnitude; and wherein the controller configures the signalgenerator to supply, as the test signal, a test voltage having a secondvoltage magnitude that is substantially less than the first voltagemagnitude.
 10. The apparatus of claim 8 wherein the connecting mediumincludes a local end and a remote end, and wherein the controllerselectively identifies, through the local end of the connecting medium,one of (i) a backwards wired device condition at the remote end, (ii) anopen condition at the remote end, (iii) a remotely powerable devicecondition at the remote end, and (iv) a shorted/non-powerable devicecondition at the remote end.
 11. The apparatus of claim 8 wherein thedifferential signal lines of the connecting medium include a first pairof differential signal lines configured to carry data signals betweennetwork devices and a second pair of differential signal linesconfigured to carry other data signals between the network devices; andwherein the controller, when configuring the signal generator to providethe test signal, is configured to: direct the signal generator to applya DC voltage across the first and second pairs of differential signallines.
 12. The apparatus of claim 11 wherein the controller, whendirecting the signal generator to apply the DC voltage across the firstand second pairs of differential signal lines, is configured to: couplethe signal generator between a centertap of the first pair ofdifferential signal lines and a centertap of the second pair ofdifferential signal lines.
 13. The apparatus of claim 11 wherein thecontroller is further configured to: direct the signal generator toprovide remote power to the computer network through the first andsecond pairs of differential signal lines to remotely power a device.14. An apparatus for discovering a powerability condition of a computernetwork, comprising: a controller; a signal generator coupled to thecontroller; and a detector coupled to the controller, the controller (i)configuring the signal generator to provide a test signal to aconnecting medium of the computer network, (ii) configuring the detectorto measure a response signal from the connecting medium of the computernetwork, and (iii) indicating whether a remotely powerable deviceconnects to the connecting medium of the computer network based on theresponse signal, wherein the connecting medium includes (i) a firstconnecting link having a local end that terminates at a firsttransformer and a remote end, and (ii) a second connecting link having alocal end that terminates at a second transformer and a remote end; andwherein the controller configures the signal generator to apply the testsignal to the connecting medium through a centertap of the firsttransformer and a centertap of the second transformer.
 15. A method fordiscovering a powerability condition of a computer network, the methodcomprising the steps of: providing a test signal to differential signallines of a connecting medium of the computer network; measuring aresponse signal from the differential signal lines of the connectingmedium of the computer network; and determining whether abackwards-wired remotely powerable device connects to the connectingmedium of the computer network based on the response signal, and when itis determined that a backwards-wired remotely powerable device connectsto the connecting medium, applying power to the backwards-wired remotelypowerable device.